Automatic oil well pump control



Feb. 28, 1967 H. W. BOYD ETAL AUTOMATIC OIL WELL PUMP CONTROL Filed Aug.25, 1965 NE MINUTE 30 MINUTES I :41

DRIVE TIMER 40 MOTOR #30 SWITCH .6; START f {1 STOP MOTOR CONTROL 22cmcun INVENTORS HARVEY W. BOYD JOSEPH I. BURLEIGH JESSIE L. ROBERSONATTORNEY S United States Patent Ofltice 3,305,210 Patented eb. 28, 19673,396,210 AUTGMATIC OIL WELL PUMP CONTROL Harvey W. Boyd, 4401 AnettaDrive; lioseph I. Eurleigh, 1205 Superior Lane; and Jessie L. Roberson,2093 W. Indiana, all of Midland, Tex. 79701 Filed 25, 1965, Ser. No.482,538 2 Claims. (Cl. 103-25) This invention relates to oil well pumpcontrols and, more particularly, it relates to means for automaticallystarting and stopping an oil well pump responsive to the presence offluid in the wellbore to thereby efliciently pump out wells whichproduce less than the capacity of the pump.

In many instances a producing oil well will have a maximum productivecapacity which is less than the capacity of the pump installed in thewell. For example, a small standard size pump has a flow pipe 1% inchesin internal diameter. This pump will displace 40 to 50 barrels per dayeven when reciprocating at slow speeds. Many wells however operate inthe production capacity range of to 20 barrels per day. In such wells itis more eflicient to run the pump intermittently only when the oil ispresent in the wellbore. It is significant that the loading on the pumpis increased when pumping a dry well.

It is characteristic of oil bearing strata that oil may seep slowly intoa wellbore over a relatively long period of time as compared with thepump out speed. Thus, a continually operating pump will tend toerratically pump and be subject to excessive wear when the store of oilin the wellbore is exhausted and it is pumping only the re sidual flowfrom the oil bearing strata into the wellbore. Although systems forautomatic pump shutdown based upon presence of fluid flow from the pumpare known,

these have not been efl'lcient or satisfactory because of the erraticconditions of sensing the partial flow as the stored oil in the wellborenears the minimum pumping level and the pumping is dependent in part onthe residual flow through the oil bearing strata.

Accordingly, it is an object of the invention to provide improved,automatic controls for starting and stoppin an oil well pump responsiveto the conditions at the downhole pump which signal presence of fluid inthe wellbore.

In accordance with the present invention therefore the loading of thepump is sensed to indicate an increased load on the doWnstroke whichoccurs when the wellbore is pumping dry. This loading is sensed bydetermining the weight or the load upon the pump rod string anddetermining when it changes as a result of pump out of the wellbore, andusing this sensed control to automatically shut down the pumping untilsuch time that enough residual oil has filtered back into the well toprovide enough of a store in the wellbore for a further pump outoperation.

A more detailed description of the invention and its mode of operationwill be found in the following specification with reference made to theaccompanying drawings, wherein:

FIGURE 1 is a diagrammatic view of an oil well pump; and

FIGURE 2 is a block control circuit diagram of an automatic pump shutdown control mechanism.

In the typical oil well pump as shown in FIGURE 1, a pumping unit or aprime mover is mounted on a tower 4 which permits the rocking beam 5 toreciprocate the pump rod string 6 against the counterbalance 7 by actionof an electric motor or engine unit (not shown). The sucker rod stringis inserted down the hole inside the tubing 8 to terminate at a downhole pump 9 which is located inside the wellbore 10. Inside the wellborea fluid level 11 is attained by oil trickling through the oil bearingstrata 12.

In general, the pump operating mechanism comprises a first travelingvalve 14 which is reciprocated with the rod string connected to thehollow plunger 15 and a second standing or stationary valve 16positioned at the end of the pump 9. Thus in operation, the weight ofthe oil inside the tubing 8 will hold the traveling valve 14 closed onthe pumping upstroke and permit the oil to be lifted up the tubing andout the flow pipe 17. During this operation the standing valve 16 willbe lifted by pressure of the oil within the well casing 10, and thetubing is filled to a level substantially equal to that of the level ofthe oil 11 within the wellbore 10. Thus, upon the downstroke thestanding valve 16 is closed when oil stands in the lower section of thepump 9 beneath the hollow plunger 15. This therefore opens the travelingvalve 14 and permits the pump to attain its downward stroke whiletransferring the oil within the lower part of the pump 9 into the hollowplunger 15 of the pump for attaining a further pump out cycle on thepump upstroke.

In accordance with the present invention this pumping action is useddirectly to sense the conditions of the bottom of the bore and provide asignal for shut down of the pump when the level of the oil 11 in thewellbore 10 falls to such an extent that the loading on the pump issignificantly increased. Consider in this respect the operation of thepump when the oil level is below that required to operate the standingvalve 16. On the normal downstroke the fluid in the lower barrel causesthe traveling valve 14 to open and transfers the fluid load or theweight of all the oil in the tubing 8 to the standing valve 16 whichthen closes. Thus, the weight of the rods or the load on the rods isless because of the loss of the weight of the oil in tubing 8 on thedownstroke than weight on the upstroke when the fluid valve 14 is closedand the rods must pull the weight of the oil in the pipe upward withinthe tubing 8. This weight transfer occurs because the plunger 15 insidethe pump 9 is essentially leak-proof containing a seal so that theentire fluid passage takes place through the valve 14.

However, if there is no fluid in the barrel as the downstroke begins,the traveling valve 14 does not open and the weight is not transferredto the standing valve 16. In a typical well installation with a lfii-inch pump installed inside a 2 /2-inch tubing and a wellborediameter of 7 inches having the pump connected to the surface with4-inch sucker rods, the weight of the rod string on the upstroke was9000 pounds with a depth of 4500 feet. This dropped to 4500 poundsduring the downstroke when the well was pumping fluid, but reverted to9000 pounds when the well was pumped dry.

For the purpose of sensing this change of weight in the rods a hydraulicload indicator 20 manufactured by the I. M. Huber Corporation wasinstalled in the rod string. This produced a hydraulic pressure signalof pounds per square inch for each 1000 pounds of rod weight. Suchpressure is carried by hydraulic line 21 to a hydraulically operatedpressure switch 22, for which the pressure shut down mechanism of theswitch was adjustable. In a typical example the pressure switch was setat 800 pounds per square inch as a threshold pressure so that thepressure switch 22 would send an electric signal at its output leadswhich can be used for shut down whenever the pressure exceeds 800 poundsper square inch. It may be seen from the foregoing data that when theoil level 11 in the wellbore 10 falls below the necessary level that theloading during the downstroke will increase to 9000 pounds and give apressure reading of 900 pounds per square inch thereby exceeding thepressure threshold level of switch 22 and sending a signal which willindicate that the pump should be shut down.

A typical control circuit for this sort of operation is shown in FIGURE2 where a drive motor 30 is operated from a three phase electricalsupply line, for example, by way of the motor control circuit 31 whichprovides for starting and stopping the drive motor. These and similarpower control units are conventionally supplied with standard oil wellrings. It is noted that in the control operation that the pressure onlyvaries on the downstroke of the pump and is always attained at the highpressure on the upstroke of the pump. Accordingly, a magnetic proximityswitch 32 is used in connection with the counterbalance mechanism 7 toindicate the downstroke position of the pump. Thus as shown in the motorcontrol circuit, the two switches 22 and 32 are used in series toprovide a stop control for the motor control circuit when the pressureswitch 22 indicates that the pressure is high on the downstroke andcloses contact 22 at the same time that the contact 32 indicates thepump is on the downstroke. Then in the normal course of events when thepump is on the upstroke and contact 22 closes it will not effectuate astopping of the drive motor through the motor control circuit stop lead.

It is thus seen that the pump mechanism may be stopped automatically bythe actual critical level of fluid encountered at the bottom of thehere. It may be readily seen that this mode of control significantlyimproves the efficiency in loading upon the pumping mechanism andprovides for pump out of the maximum capacity of any well which has acapacity or a productive flow which is less than the full capacity ofthe pumping mechanism.

In order to make the system fully automatic, the start control for thedrive motor is operated by means of a timer switch 40, which serves toprovide a typical periodic on-otf cycle such as shown in Waveform 41where the switch 42 is closed to start the drive motor and maintain itin operation for only one minute at a repetitive cycle of perhaps 30minutes. This assures that the pump will be operating normally beforeautomatic shut down control is eifectuated by means of the controlswitches 22' and 32' previously described. The timer switch 40 may besimply a clock motor with appropriate cam and switch set selected toclose the switch during chosen intervals which can be set to correspondto the capacity of a particular well. For example, if the well has acapacity that requires pumping for 10 minutes before shutting down, thetimer will permit the well to be held in shut down condition for 20minutes while more fluid is accumulating in the wellbore by seepagethrough the oil bearing strata. Then the pump will be started foranother automatic pumping cycle and in this manner the maximum capacitymay be realized from the well by automatic cycling of the pump drivemechanism.

It may be recognized in accordance with the teachings of the presentinvention that the method of controlling the pump shut down iseffectuated by conditions existing at the bottom of the well asindicated by the measure of the weight or the loading upon the pump rodassembly or the pumping mechanism itself which changes significantlyduring the downstroke during conditions when the fluid is present andwhen the fluid is absent. Therefore, in accordance with the teachings ofthe present invention various types of weight sensing devices and shutdown control circuits could be used without departing from the spirit orthe scope of the invention. For example, a strain gauge could be mountedupon the pump rods to indicate the difference in loading to replace thehydraulic senser. Those novel features believed descriptive of the scopeand the nature of the invention are defined with particularity in theappended claims.

What is claimed is:

1. Control means for a motor driven reciprocating rod type of oil wellpump which exhibits the property of increasing the load on the pump rodon the downstroke when the Well fluid is below pumping level comprisingin combination, means for sensing an increase in the weight of the pumprod string, switch means operable by the sensing means at a thresholdwhen the weight exhibited by the rod string on the downstroke increasesto substantially that on the upstroke, and means shutting down the pumpmotor responsive to operation of said switch for a time periodpermitting fluid to enter the well and reach said pumping level.

2. Control means as defined by claim 1 wherein the switch means includesone switch actuated by position of the pump rod on the downstroke andanother switch actuated responsive to said threshold, and wherein thecontrol means includes a circuit connecting the two switches in seriescircuit with the means shutting down the pump motor.

References Cited by the Examiner UNITED STATES PATENTS 2,456,456 12/1948Smith 103-25 2,661,697 12/1953 Long et al 10325 2,947,931 8/1960 Hubby10325 X 3,225,697 12/1965 Brown 10325 ROBERT M. WALKER, PrimaryExaminer.

1. CONTROL MEANS FOR A MOTOR DRIVEN RECIPROCATING ROD TYPE OF OIL WELLPUMP WHICH EXHIBITS THE PROPERTY OF INCREASING THE LOAD ON THE PUMP RODON THE DOWNSTROKE WHEN THE WELL FLUID IS BELOW PUMPING LEVEL COMPRISINGIN COMBINATION, MEANS FOR SENSING AN INCREASE IN THE WEIGHT OF THE PUMPROD STRING, SWITCH MEANS OPERABLE BY THE SENSING MEANS AT A THRESHOLDWHEN THE WEIGHT EXHIBITED BY THE ROD STRING ON THE DOWNSTROKE INCREASESTO SUBSTANTIALLY THAT ON THE UPSTROKE, AND MEANS SHUTTING DOWN THE PUMPMOTOR RESPONSIVE TO OPERATION OF SAID SWITCH FOR A TIME PERIODPERMITTING FLUID TO ENTER THE WELL AND REACH SAID PUMPING LEVEL.